Quenching apparatus for use with thermal cracking system

ABSTRACT

The quenching apparatus is composed of a header and cooling pipes. The header consists of a plurality of relatively closely spaced, hollow frustoconical members having a smaller diameter that communicated with a conduit in the furnace and a larger diameter that communicates with the cooling pipes. The conical members are disposed coaxially and have radiating fins thereon.

United States Patent Inventors lchiro Tokumitsu;

Mitsumaro Okamura,Tokuyama-shi,

Yamnguchi-ken, Japan Appl. No. 769,009 Filed Oct. 21, 1968 Patented Jan.,5, 1971 Assignee ldemitsu Petrochemical Co., Ltd. Priority Nov. 29, 1967 Japan No.42/99727 QUENCHINGAPPARATUS FOR USE WITH THERMAL CRACKING SYSTEM 1 Claim, 4 Drawing Figs.

U.S. Cl. 165/174, 196/138, 208/48, 208/95, 23/284 Int. Cl. F28d 7/00 Field of Search 196/138, 140, 127, 128; 23/284; 165/175, 174; 202/227,

caAcxms FURNACE 1561 References Cited UNITED STATES PATENTS 1,130,318 3/1915 Moore 196/138X l,6l3,0l6 1/1927 Brandt 196/138X 2,813,700 11/1957 Schenck 165/l75X Primary Examiner- Norman Yudkoff Assistant Examiner- David Edwards Anorneys- Harry C. Bierman, Jordan B. Bierman and Bierman and Bierman ABSTRACT: The quenching apparatus is composed of a header and cooling pipes. The header consists of a plurality of relatively closely spaced, hollow frustoconical members having a smaller diameter that communicated with a conduit in the furnace and a larger diameter that communicates with the cooling pipes. The conical members are disposed coaxially and have radiating i'ms thereon.

2 comcm.

MEMBERS PATENTED JAN 5197! SHEET 2 BF 2 HEAT IO EXCHANGER 12 comcm.

MEMBERS CRACKING f FURNACE IIvYJNTMJ I37: gain): a

QUENCHING APPARATUS FOR USE WITH THERMAL CRACKING SYSTEM The invention relates to apparatus for quenching gas effluents from a thermal cracking system for hydrocarbons.

Hydrocarbons such as naphtha are heated in such systems together with water vapor to elevated temperatures to cause thermal cracking for the production of ethylene, propyrene or the like. Gas effluents from such system are usually conveyed to a quenching heat exchanger through a funnel-shaped hollow channel that is connected between the conduit from the system and the individual inlets of a number of cooling pipes in the heat exchanger. The thermal cracking reaction of naphtha is completed within a very short period, and the product is extremely unstable because of high temperatures and high partial pressure of unsaturated hydrocarbons such as ethylene in the effluent gas. When such product is maintained at high temperatures for a long period, secondary and tertiary reactions are caused to produce carbon deposits in the piping and to reduce the yield. The carbon deposits reduce the cooling efficiency of the heat exchanger and also cause difficulties in operating the system and heat exchanger. Thus the system must be often interrupted to remove or burn the deposited carbon by oxidation with air and the heat exchanger has to be dismounted for mechanical scavenging. Obviously this results in a decreased rate of operation and thermal stresses due to variation of temperature, the latter causing wear of material. In addition, the dismounting involves mechanical damages. For these reasons, the product of the. thermal cracking process must be rapidly cooled to a given temperature. in the prior art sy'st em, however,'the channel fans out sharply from the outlet onduit of arelatively smalldiameter of the thermal cracking ystern tofaiiargediarnelter,which may encompass as many as 500'coolingpipes of the'heat eirchanger, sothat the effluent flow through the conduit comes to stagnation in the channel, with consequent poor flow rate through the heat exchanger.

It is an object of the invention to provide an apparatus for quenching gas effluents from a thermal cracking system for hydrocarbons in which the stagnation of effluent flow in a channel upstream of a quenching heat exchanger and secondary reaction of the effluent gas are minimized.

The apparatus according to the invention comprises a nected with cooling pipes 9 in a heat exchanger generally indicated M10. The header and guide tubes are made from heat-resistant steel such as nickel-chrome steel.

in use, raw material hydrocarbons are fed together with water vapor through the supply pipe 3 and heated to a temperature between 750 and 950C. during passage through the heating pipe 2, whereby thermal cracking reaction proceeds. Gas effluents resulting from this reaction are conveyed through pipe 2 to the header 4 where the effluent flow is diyided into a plurality of guide tubes 8 and thence to the coolmg pipes 9 o the heatexchanger 10. it will be understood that the diameter of the guide tubes 8 is chosen to minimize pressure loss. In an example, when the apparatus shown was used in place of the hollow channel of the type mentioned above with the same heat exchanger, the time interval between successive scavenging of the heat exchanger increased from 20 days to 70 days.

Referring to FIGS. 3 and 4, the embodiment shown comprises a channel assembly 11 which includes a plurality of truncated cone members of different sizes arranged in concen quenching heat exchanger including a number of cooling pipes having individual inlet openings at one end for admission of gas effluents, and is characterized by the provision of means controlling the flow of gas effluents. from the thermal cracking system in a manner such that the gas flow is divided into a plurality of separate contiguous passageways before being supplied to the cooling pipes.

The invention will be described with reference to the drawings, in which FIG. I is a schematic view of a thermal cracking system and an apparatus according to one embodiment of the invention,

FIG. 2 is a section along the line A-A in FIG. 1,

FIG. 3 is a view similar to F IG'. 1 showing another embodiment of the invention, and

FIG. 4 is a perspective view of a channel assembly shown in tric relationship. The outermost cone member has a bottom pipe portion which is connected at ajoint 5 with the pipe 2 extending from the thermally cracking furnace l. Adjacent cone members 12 are interconnected by struts IS. The members 12 are made from heat-resistant steel sheet.

Although the reason of the success with the invention is not completely understood, it is considered that the construction shown prevents or minimizes sudden expansion of the effluent gas from the thermal cracking system at the junction with the heat exchanger or in the hollow funnel-shaped channel used in the prior art, thereby preventing occurrence of vortex or similar turbulent flow and thus enabling a substantially uniform flow profile.

We claim:

1. Apparatus for quenching gas effluents from a thermal cracking system for hydrocarbons, comprising a quenching heat exchanger which includes a number of cooling pipes having individual inlet openings at one end for admission of gas effluents, and a plurality of relatively closely spaced, hollow frustoconical members of heat-resistant material having a smaller diameter and a larger diameter, said conical members being disposed coaxially and one within another, the outermost one of the members being connected at its smaller diameter end to a conduit in the thermal cracking system for supply of said gas effluents into said conical members, the larger diameter end of the members being in communication with the inlet openings of the cooling pipes in said heat exchanger. 

1. Apparatus for quenching gas effluents from a thermal cracking system for hydrocarbons, comprising a quenching heat exchanger which includes a number of cooling pipes having individual inlet openings at one end for admission of gas effluents, and a plurality of relatively closely spaced, hollow frustoconical members of heat-resistant material having a smaller diameter and a larger diameter, said conical members being disposed coaxially and one within another, the outermost one of the members being connected at its smaller diameter end to a conduit in the thermal cracking system for supply of said gas effluents into said conical members, the larger diameter end of the members being in communication with the inlet openings of the cooling pipes in said heat exchanger. 